Mr Barr addressed ACT Labor's annual conference on Saturday morning, laying down the foundations for the party's election platform with a commitment to grow the territory's public service and retain government assets - including ACTION buses and CIT - if it is returned at the October 2020 ballot.

The Chief Minister used the speech to attack the Liberals' stance on social issues, drawing particular attention to Alistair Coe's opposition to marriage equality during the 2017 postal vote.

Speaking to reporters outside the conference, Mr Barr said the next territory election would be fought not just on policy grounds, but on the differences between the major parties' "philosophical starting point and outlook".

"I will be reminding progressive voters that the Canberra Liberals are extremely conservative, but I don't really need to do that very often because the Canberra Liberals do that themselves every day," Mr Barr said.

Labor is aiming to be returned for a sixth term in office, which would extend its time in power into a third decade.

Mr Barr said the "it's time factor" could work against Labor at the next election, acknowledging that the "longer anyone is in government, the more difficult it is."

The Canberra Liberals have already pledged that, if elected at next October's vote, they would freeze rates for its first term and abolish payroll tax.

Mr Coe has insisted that a Liberal government would not have to cut the public service in order to cover for the lost revenue.

At Saturday's Labor conference, Mr Barr cast doubt over Mr Coe's assurance.

"I guess the best predictor of future behaviour is past behaviour and the Liberal party have form in this city and in every jurisdiction across this country, that they will choose privatisation and outsourcing," he said.

The Canberra Times sought comment from Mr Coe on Saturday, but was told he was unavailable.